Device in a brake unit

ABSTRACT

An electromechanical brake unit in a housing (1) is provided with a drive sleeve (8) subjected to a torque of a prestressed coil spring (6), a locking spring (16) between the drive sleeve and the housing for permitting rotation of the former in a first direction, and a control sleeve (17), which is rotatable by a control motor (20) in the first direction to open the locking spring and allow the drive sleeve to rotate the same angular distance as the control sleeve. In order to obtain rotary force transmission from the drive sleeve (8) over the locking spring (16), if the control sleeve (17) is not held against rotation, the locking spring has a slightly smaller external rest diameter than the bore in the housing (1), with which it is to cooperate, whereas the control motor (20) is provided with means to hold it against rotation in its rest position, unless the current supply is broken.

TECHNICAL FIELD

This invention relates to a brake unit--preferably but not exclusivelyfor a rail vehicle--including a housing, a drive sleeve subjected to atorque of a prestressed coil spring, a locking spring between the drivesleeve, to which it is attached, and the housing for permitting rotationof the former in a first direction, and a control sleeve, which isrotatable by a control motor in the first direction to open the lockingspring, connected to the control sleeve with one end, and allow thedrive sleeve concentric therewith to rotate the same angular distance asthe control sleeve.

BACKGROUND OF THE INVENTION

A brake unit of this kind, where the, coil spring is "loaded" by anelectric motor and there is a further locking spring and a ball screwarrangement to transform the rotary motion into an axial movement, isshown and described in our EP-A-0 334 434. This electro-mechanical brakeunit, in which both the brake energy and the control signal are suppliedin electric form, has great advantages over both more conventional brakeunits, which are pneumatically supplied and controlled, and earlierattempts with electro-mechanical brake units.

However, the electro-mechanical brake unit as shown and described inEP-A-0 334 434 has the characteristic that a current supply to thecontrol motor therein is required to obtain brake application under theaction of the prestressed coil spring. This means that the brake unitdoes not have the safety feature with automatic brake application at theloss of the control current supply, which in this case thus is electric.

In certain instances it is a prerequisite with this feature, which inpneumatic installations often is obtained by means of a so called springbrake actuator. The feature does not only provide the necessary safetyat the loss of the control current supply, but it may also give a simpleand effective way of obtaining a parking brake.

THE INVENTION

In an electro-mechanical brake unit of the kind described above thedesired safety and parking brake feature may according to the inventionbe attained in that the locking spring has a slightly smaller externalrest diameter than the bore in the housing, with which it is tocooperate, but normally is held in engagement with the bore by thetorque from the drive sleeve, and in that the control motor is providedwith means to hold it against rotation in its rest position, unless thecurrent supply is broken.

The preferred way of obtaining the feature with the holding of thecontrol motor against rotation in its rest position is that the motor isprovided with an electrically controlled brake, preferably anelectro-magnetic brake.

Alternatively, the control motor can be held against rotation by meansof a certain current supply to its windings.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in further detail below reference beingmade to the accompanying drawing, which in a side view, partly insection, shows an actuator, namely an electro-mechanical brake unit,according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

An actuator or electro-mechanical brake unit according to the inventionis basically the same as is described in EP-A-0 334 434.

A relatively brief description of the overall design is therefore givenhere, and reference is made to the earlier publication. Emphasis is puton the improvement afforded by the present invention.

The electro-mechanical brake unit has a housing 1 with lids 2 and 3. Theunit is also provided with a force transmitting member 4, axiallymovable in relation to the housing 1. The housing 1 and the member 4 areprovided with attachments 5 for the mounting of the unit, for example ina conventional disc brake caliper of a rail vehicle.

A powerful coil spring or clock spring 6 is arranged in the housing 1.The outer end of the spring 6 is anchored to a rotatable motor sleeve 7and its inner end to a rotatable drive sleeve 8, which is journalled inthe housing 1.

An electric motor 10, attached to the housing 1, is drivingly connectedto a gear ring 7' on the motor sleeve 7. A locking spring 12 enables themotor sleeve 7 only to be rotated in the direction for tightening thecoil spring 6.

Coaxial with the drive sleeve 8 is a rotatable drive ring 13 in splinedengagement with a spindle ring 14, which is attached to a rotatablespindle 15.

A rotary force transmission between the drive sleeve 8 and the drivering 13 is performed by means of an arrangement consisting of threeconcentric members, namely an outer locking spring 16, a control sleeve17, and an inner locking spring 18.

The outer end of the control sleeve 17 is provided with a gear ring 17'in engagement with corresponding gears on the rotary motor shaft 19 ofan electric control motor 20 attached to the lid 3. The shaft 19 of themotor 20 is provided with a disc 21 cooperating with a fixed yoke 22.The disc 21 has circumferential holes for counting by the yoke 22 andthereby control of the rotation of the control motor 20.

A force transmitting sleeve 23 is attached to the force transmittingmember 4. A ball nut 25, which together with the spindle 15 forms a ballscrew, is non-rotatably attached to the force transmitting sleeve 23.The spindle 15 is journalled in the force transmitting sleeve 23 bymeans of a radial ball bearing 26 and in a force sensing cup 27 by meansof a ball bearing 28.

An elastic disc 30 is confined between the force sensing cup 27 and thelid 3. A pressure transducer 31 is arranged in the lid 3 in contact withthe elastic disc 30.

The interaction between the different parts, especially the two lockingsprings 16 and 18 and the control sleeve 17, is now to be described.

The outer locking spring 16, which can also be called an applicationspring for reasons apparent below, serves to prevent the drive sleeve 8from rotating relative to the housing 1 in one direction, and its lefthand end is locked to the drive sleeve 8. In the prior device accordingto EP-A-0 334 434 the major part of the spring 16 is arranged with itsouter surface in contact with coaxial cylindrical inner surfaces of thesleeve 8 and the housing 1, which in other words means that the restdiameter of the spring is larger than the diameter of said innersurfaces. In the new device the spring 16 has a rest diameter which isslightly smaller than the diameter of said inner surfaces and willaccordingly not be in contact with the housing 1, provided that noexternal torque is applied to it. A few turns of the locking spring 16has a smaller diameter and are with its inner surface in engagement withthe outer surface of the cylindrical control sleeve 17.

The inner locking spring 18, which can also be called a release spring,serves to transmit rotational movement in one direction between thedrive sleeve 8 and the drive ring 13 but also establishes a means fortransmitting rotational movement in the other direction between thecontrol sleeve 17 and the drive ring 13. The inner surface of thelocking spring 18 is in contact with coaxial cylindrical outer surfacesof the drive sleeve 8 and the drive ring 13. The right hand end of thespring 18 is locked to the drive ring 13, whereas its left hand end isprovided with an upwardly projecting end 18' engaging an axialprojection 17" at the left hand end of the control sleeve 17. In orderto protect the control motor 20, the spring 18 may--as an alternative tobeing provided with the projecting end 8'--have a few turns to the leftwith a larger diameter engaging the control sleeve 17.

The function of the arrangement so far described is as follows: Assumingthat the coil spring 6 is tensioned or wound up by the electric motor 10and backwards rotation of the latter is prevented by the one-waycoupling 12, the drive sleeve 8 is subjected to a large torque in onerotational direction. Provided that the control sleeve 17 is heldagainst rotation by means in or at the control motor 20, this rotationalmovement will increase the diameter of the application spring 16, sothat the sleeve 8 is locked against rotation in this direction by thespring.

By turning the control sleeve 17 (by means of the control motor 20) itis, however, possible to "open" the application spring 16, i.e. to turnit in the direction opposite the locking direction, by means of thespring turns in engagement with the control sleeve 17. Hereby the drivesleeve 8 will be free to turn under the action of the coil spring 6until the application spring 16 again locks the sleeve 8 to thehousing 1. The turning movement of the drive sleeve 8 corresponds inother words to that of the control sleeve 17. During this turningmovement the inner locking spring 18--due to its lockingdirection--transmits the turning movement and the torque to the drivering 13.

The torque transmitted to the drive ring 13 is transferred through theball screw spindle 15 to an axial force in the ball nut 25, the forcetransmitting sleeve 23 and the force transmitting member 4. Theapplication stroke or movement is to the left in the drawing.

The drive sleeve 8 can rotate (for transmitting its torque to the drivering 13 via the inner locking spring 18) when and to the extent thecontrol sleeve 17 is rotated by the control motor 20 in the unlockingdirection for the application spring 16 but also--due to the fact thatthe application spring 16 is not in contact with the housing 1 in itsrest position--when the control motor 20 is not held against rotation.

As has appeared, the control motor 20 serves to control the applicationstroke (but also the release stroke). However, if the control motor isnot positively held against rotation or rotated under control, a torquefrom the drive sleeve 8 will be transmitted through the applicationspring 16, which is hereby not in locking contact with the housing 1.The purpose of this design is to accomplish the safety feature that anapplication stroke occurs if the current supply to the control motor 20is broken for any reason. A simple parking brake feature is alsoobtained.

There are at least two alternatives for preventing the control motorshaft 19 from rotating, namely either to provide the control motor 20with an electro-magnetic brake (which is released at the lack of currentsupply) or to supply the motor windings with a holding current in a restposition.

The release stroke or movement of the force transmitting member 4 andsleeve 23 to the right in the drawing is properly described in EP-A-0334 434, to which reference is made. The release stroke is not affectedin principle by the modification of the application spring 16 and thefunction of the control motor 20.

As an alternative to drive sleeve control by means of a motor, it ispossible to obtain the same result by means of electro-magnets. In sucha case the relevant electro-magnet is kept in its sleeve holdingposition, unless the current supply is broken. This alternative isintended to be covered by the language of the main claim.

I claim:
 1. In a brake unit, including a housing (1), a drive sleeve (8)subjected to a torque of a prestressed coil sleeve (6), a locking spring(16) positioned in a bore in housing (1) between the drive sleeve, towhich it is attached, and the housing for permitting rotation of theformer in a first direction, and a control sleeve (17), which isrotatable by an electric control motor (20) having a current supplythereto in the first direction to open the locking spring, connected tothe control sleeve with one end, and allow the drive sleeve concentrictherewith to rotate the same angular distance as the control sleeve, theimprovement providing for automatic application of the brakes in theevent that drive current to the control motor (20) is interrupted,comprising in combination: said locking spring (16) being provided witha slightly smaller external rest diameter than the bore in the housing(1) normally held in engagement with the bore by the torque from thedrive sleeve (8), and wherein the control motor (20) is provided withmeans comprising said locking spring (16) rest diameter to hold thespring (16) locked in engagement with said bore in said normal position,and to return the locking spring (16) to its rest diameter when thecentral motor current supply is broken whereby the brakes are applied.2. A brake unit according to claim 1, wherein the control motor (20)comprises an electro-magnet.
 3. A brake unit according to claim 1,wherein the control motor (20) is held against rotation in a restposition by means of normally unbroken current from said current supply.